| Issue |
A&A
Volume 672, April 2023
|
|
|---|---|---|
| Article Number | A123 | |
| Number of page(s) | 14 | |
| Section | Catalogs and data | |
| DOI | https://doi.org/10.1051/0004-6361/202245484 | |
| Published online | 10 April 2023 | |
Discovering strongly lensed quasar candidates with catalogue-based methods from DESI Legacy Surveys★
1
Key lab of Space Astronomy and Technology, National Astronomical Observatories,
20A Datun Road, Chaoyang District,
Beijing
100012,
PR China
e-mail: zzhe@nao.cas.cn; nan.li@nao.cas.cn
2
School of Astronomy and Space Science, University of Chinese Academy of Sciences,
No. 1 Yanqihu East Rd, Huairou District,
Beijing
100049,
PR China
3
National Astronomical Observatories, Chinese Academy of Sciences,
20A Datun Road, Chaoyang District,
Beijing
100012,
PR China
4
School of Physics and Astronomy, Nottingham University,
University Park, Nottingham
NG7 2RD,
UK
Received:
17
November
2022
Accepted:
25
January
2023
Context. The Hubble tension, revealed by a ~5σ discrepancy between measurements of the Hubble-Lemaitre constant among observations of the early and local Universe, is one of the most significant problems in modern cosmology. In order to better understand the origin of this mismatch, independent techniques to measure H0, such as strong lensing time delays, are required. Notably, the sample size of such systems is key to minimising the statistical uncertainties and cosmic variance, which can be improved by exploring the datasets of large-scale sky surveys such as Dark Energy Spectroscopic Instrument (DESI).
Aims. We identify possible strong lensing time-delay systems within DESI by selecting candidate multiply imaged lensed quasars from a catalogue of 24 440 816 candidate QSOs contained in the ninth data release of the DESI Legacy Imaging Surveys (DESI-LS).
Methods. Using a friend-of-friends-like algorithm on spatial co-ordinates, our method generates an initial list of compact quasar groups. This list is subsequently filtered using a measure of the similarity of colours among a group’s members and the likelihood that they are quasars. A visual inspection finally selects candidate strong lensing systems based on the spatial configuration of the group members.
Results. We identified 620 new candidate multiply imaged lensed quasars (101 grade-A, 214 grade-B, 305 grade-C). This number excludes 53 known spectroscopically confirmed systems and existing candidate systems identified in other similar catalogues. When available, these new candidates will be further checked by combining the spectroscopic and photometric data from DESI.
Key words: gravitational lensing: strong / quasars: general / methods: data analysis / catalogs / surveys
The catalogues and images of the candidates are only available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/672/A123
© The Authors 2023
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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